The Sun's Structure and Layers

Study Notes

The Sun is divided into several layers, each with distinct characteristics and processes.

The core is the central region of the Sun, making up about 25% of its radius.
It has a temperature of around 15 million°C (27 million°F).
Nuclear reactions occur in the core, where hydrogen atoms fuse to form helium, releasing vast amounts of energy.

The radiative zone surrounds the core, extending from 0.25 to 0.7 solar radii.
Energy generated in the core travels through the radiative zone via radiation.
Photons emitted by the core interact with the dense plasma, causing them to be absorbed and re-emitted multiple times.

The convective zone occupies the outer 30% of the Sun's radius.
Energy is transferred through convection, where hot, ionized gas (plasma) rises to the surface, cools, and then sinks back down.
This process allows energy to be transported efficiently from the core to the surface.

The photosphere is the visible surface of the Sun, with a temperature around 5,500°C (10,000°F).
It is the layer that we can see, and is the source of sunlight.
The photosphere is a few hundred kilometers thick.

The chromosphere is the layer above the photosphere, extending several thousand kilometers.
It is visible during total solar eclipses, appearing as a pinkish ring around the Sun.
The chromosphere is where ultraviolet (UV) and X-rays are emitted.

The corona is the outer atmosphere of the Sun, stretching millions of kilometers into space.
It has a temperature of around 1-2 million°C (1.8-3.6 million°F), much hotter than the surface.
The corona is visible during solar eclipses, appearing as a bright, white halo.

The Sun's core is incredibly hot, with temperatures reaching over 15 million degrees Celsius (27 million degrees Fahrenheit).
At these extreme temperatures, nuclear fusion reactions occur, which involve the combination of atomic nuclei (usually isotopes of hydrogen) to release vast amounts of energy.
The most common fusion reaction in the Sun's core is the proton-proton chain reaction, which involves the fusion of hydrogen nuclei (protons) to form helium.
This reaction begins with the collision of two protons, resulting in the formation of a deuterium nucleus (a proton and a neutron) and a positron (the antiparticle of an electron).
A second proton then collides with the deuterium nucleus, forming a nucleus of helium-3 and releasing another positron.
Finally, two helium-3 nuclei collide to form a nucleus of helium-4, releasing two protons in the process.
The energy released in these reactions is in the form of light and heat, which is then radiated outward from the core through the Sun's interior and atmosphere.
The proton-proton chain reaction is responsible for producing about 99% of the Sun's energy output.